1. The Field of the Invention
The invention relates to a tool for producing a thread, in particular an internal thread.
2. Background and Relevant Art
For thread production, in particular for producing threads for screwed connections, tools working with a cutting action and tools working with a chipless action are known.
Tools working with a cutting action have cutting edges. This group includes drills, which process a workpiece in particular with a continuous cut or with continuous engagement of the cutting edges in the material, and milling cutters, which process the workpiece in particular with a discontinuous or interrupted cut or with discontinuous engagement of the cutting edges in the material.
For chipless (or: forming) thread production, thread-producing tools are known which are based on forming of the workpiece and produce the thread in the workpiece by pressure. Coming within the scope of these chipless thread producers are “thread formers” in which pressing lobes (or: forming wedges) projecting outward are used for forming the material of the workpiece.
The tools normally have a tool shank and a working region formed on said tool shank. The tool shank is at least of approximately cylindrical design as a rule, and is accommodated and held in the chuck of a thread-producing device. The working region has the cutting or non-cutting features, for example cutting edges or pressing lobes, provided for the thread production or rework.
To produce a thread in an already existing bore, the tool, with the working region in front, is inserted into the workpiece or bore in the workpiece with a corresponding feed axially-relative to the longitudinal axis of the tool shank, and while rotating about this longitudinal axis. In the process, the cutting edges or pressing lobes are pressed into the surface of the workpiece or the bore. The cutting features (cutting edges) remove material in the process, and the non-cutting features (pressing lobes) press the material of the workpiece away mainly radially, that is to say perpendicularly to the longitudinal axis of the bore or to the tool axis. In the latter case, some of the material deformed in this way is consolidated; another portion is forced into the depressions or furrows between the pressing lobes of the thread former, as a result of which a thread is finally produced in the workpiece.
Both cutting and forming regions may be designed specifically for purely axial processing of the workpiece; that is to say, the respective working region or the tool is merely rotated about the tool axis, and moved into the workpiece with an axial feed. Furthermore, both cutting and forming working regions may be designed specifically for circular processing of the workpiece; that is to say, in addition to the rotation about the tool axis and the feed into the workpiece, the respective working region or the tool is also rotated in a circular manner about a further axis running parallel to the tool axis and offset from the tool axis. In addition to its own rotation, the tool therefore performs a spiral movement into the workpiece.
For purely axial processing, the cutting or forming features are normally arranged on the tool in such a way as to run at least essentially spirally around the tool axis, that is to say with a pitch along the tool axis. This arrangement ultimately constitutes the mating form of the thread to be produced; the pitch of the arrangement constitutes the thread pitch. For a circular movement, however, the arrangement is normally annular, that is to say without a pitch.
The advantage of the chipless tools is that, due to the deforming of the surface and the consolidation associated therewith, the hardness of the material in the region of the thread profile increases and thus a more wear-resistant thread is produced. However, a disadvantage with purely chipless thread production, that is to say, with thread production in which the thread is formed entirely by means of the pressing lobes, is the high loads and the associated high wear of the pressing lobes.
In order to reduce this load, it is therefore known to initially produce the thread in a prior operation. The thread may be initially produced by a cutting tool, so that the advantages of cutting and chipless thread production can be combined in this two-stage process for thread production. In this case, however, at least two separate operations using different tools are necessary.
Furthermore, Patent Application DE 10 2005 022 503.9 has disclosed a combination tool which works with both a cutting and a chipless action, and, to this end, has at least one cutting edge and at least one thread-forming region. With such a tool, the combined, that is to say both cutting and forming, thread production can be carried out by a single tool in one operation in a time and cost-saving manner. A disadvantage in this case, however, is that workpiece chips produced by the cutting region may be pressed into the thread by the following thread-forming region, which may lead to undesirable defects in the thread.